In this part III I want to visualize the rebalance operation (with 3 power values: 2,6 and 11) after disks have been added and dropped (at the same time).

To do so, on a 2 nodes Extended Rac Cluster (11.2.0.4), I added 2 disks and dropped 2 disks (with a single command) into the DATA diskgroup (created with an ASM Allocation Unit of 4MB) and launched (connected on +ASM1):

alter diskgroup DATA rebalance power 2; (At 02:11 PM).

alter diskgroup DATA rebalance power 6; (At 02:24 PM).

alter diskgroup DATA rebalance power 11; (At 02:34 PM).

And then I waited until it finished (means v$asm_operation returns no rows for the DATA diskgroup).

Note that 2) and 3) interrupted the rebalance in progress and launched a new one with a new power.

The ASM rebalance activity is not recorded into the v$asm_disk_iostat view. It is recorded into the v$asm_disk_stat view. So, if you are using the asm_metrics utility, you have to change the asm_feature_version variable to a value > your ASM instance version.

I tested with compatible.asm set to 10.1 and 11.2.0.2 and observed the same behaviour for all those metrics.

Conclusion of Part III:

Nothing surprising except (at least for me) that the Avg By/Read is stucked to 1MB (While the allocation unit is 4MB).

We visualized that the compacting phase of the rebalance operation generates much more activity on the other disks compare to near zero activity on the dropped and new disks.

I’ll update this post with ASM 12c results as soon as I can (if something new needs to be told).